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HPV infections fell by half in teen girls after vaccine, study shows

Infections with the human papillomavirus tied to cervical cancer fell by more than half in U.S. teen girls after the HPV vaccine was introduced in 2006, despite high-profile controversy -- and low rates of uptake, a new study shows.

Government health officials said Wednesday that the new data should encourage wider acceptance of the vaccine, which became a lighting rod for political controversy almost from the moment it was implemented.

Texas Gov. Rick Perry issued a 2007 executive order mandating that all sixth-grade girls be required to get HPV vaccinations, a move he later disavowed, and in 2011, Rep. Michele Bachmann ignited a firestorm by raising questions about the safety of the vaccine and whether it could cause "mental retardation."

Even now, only about a third of U.S. teen girls ages 13 to 17 have had the full series of shots that prevent HPV infection, despite repeated studies that show the vaccine is safe and effective, said Dr. Tom Frieden, director of the Centers for Disease Control and Prevention. Other countries, including places such as Rwanda, have higher HPV vaccination rates than the U.S., he added.

“The report should be a wake-up call to our nation to protect the next generation by increasing HPV vaccination rates,” said Frieden. "These are striking results because we can protect the next generation of adolescents and girls against cancer."

Rates of HPV infection targeted by the vaccine fell from 11.5 percent in 2003 to 2006 to 5.1 percent from 2007 to 2010 in girls and women ages 14 to 19, a decline of 56 percent, according to new data published in the Journal of Infectious Diseases. The effectiveness of getting at least 1 shot in the three-dose series was 82 percent, the study concluded.

That proves that the HPV vaccine works well in that target group, Frieden added. If the U.S. had reached a rate of 80 percent vaccination, some 50,000 lifetime cases of cervical cancer could be prevented, Frieden said.

“For every year we delay in doing so, another 4,400 girls will develop cervical cancer in their lifetimes,” he added.

About 79 million Americans, most in their late teens and early 20s, are infected with HPV. Each year, about 14 million people become newly infected, the CDC says. About 56 million doses of HPV vaccine have been administered in the U.S. since 2006, Frieden noted.

About 19,000 cancers caused by HPV infections occur in women in the U.S. each year, according to the CDC, with cervical cancers being the most common. About 8,000 cancers caused by HPV occur each year in U.S. men; throat cancers are most common.

The new study, led by CDC medical epidemiologist Dr. Lauri Markowitz, used data from the National Health and Nutrition Examination Survey, or NHANES, to compare prevalence of certain types of HPV infection in girls and women ages 14 to 59 before and after the 2006 launch of the HPV vaccine.

Results showed the vaccine actually worked better than expected to cut overall HPV rates in girls and women aged 14 to 19. There was no difference in other age groups over the time periods, the study found.

"The decline in vaccine-type prevalence is even better than we hoped for," Frieden said.

That could be in part because girls and women who are sexually active sought out the vaccine more often, contributing to the lower prevalence, Markowitz said.

There are two HPV vaccines, Cervarix and Gardasil. Gardasil targets HPV strains 6, 11, 16 and 18 to protect against cervical, vaginal, vulvar and anal cancer and genital warts. Cervarix targets HPV strains 16 and 18 and protects girls and women against cervical cancer. Only Gardasil is available for males.

Routine vaccination is recommended starting at age 11 or 12 for both boys and girls, but recent national immunization surveys show that only about half of all girls in the U.S. -- and far fewer boys -- have gotten even first dose of HPV vaccine, the CDC said.

Vaccination rates remain low in part because providers don't recommend them strongly enough and because some parents are reluctant to administer them, Frieden said. Parents worry about the safety of the vaccine and about immunizing children who are not sexually active.

He noted that the vaccine must be administered early, before sexual activity starts, for best effect and that repeated studies have shown HPV vaccines are as safe as other vaccines recommended for that age group. Most common side effects are minor and include fainting, dizziness and redness and pain at the injection site. CDC has not been able to link serious adverse events or deaths to the HPV vaccine, said Dr. Cindy Weinbaum, a medical epidemiologist.

"I think we owe it to the next generation -- our sisters, our daughters and our patients -- to protect them against cancer," Frieden said.

JoNel Aleccia is a health reporter at NBCNews.com. Reach her on Twitter at @JoNel Aleccia or send her an email.